While conducting certain operations downhole, it becomes necessary to relocate a packer from one elevation to another. In the past, resettable packers have employed an actuation system involving sequential griping and release of balls dropped from the surface at a particular point. The seating of the ball allowed pressure buildup behind the ball with subsequent movement of the internal components allowing selective inflation or deflation of the packing element to effectuate sealing off of the well bore. Typical of such packers are U.S. Pat. Nos. 4,823,882 and 4,893,678. Other packers or bridge plugs have been set and released by a combination of numerous interengaging components which are actuated by physical forces applied to them or by fluid pressure. Typical of such packers or bridge plugs are U.S. Pat. Nos. 4,898,239 and 4,796,707.
The disadvantages of the known designs range from their initial complexity and cost of construction to the time delays encountered by the dropping ball method of operation. There are delays associated with injecting and pumping a ball from the surface to a seat located downhole so that pressure can be built up behind the ball to initiate mechanical movement of the internal components. These delays can be as long as one to two hours to seat the ball. If this type of packer needs to be reset, the same delays must be repeated.
Another disadvantage of the designs involving dropping balls is that the seat must be constructed of a retractable nature so that the ball can be selectively released. The flow through the tool and repetitive operations could result in imperfect seating due to wear on the ball or failure of the seat elements to snap back into the position where they are properly located to effectuate a seat with the ball.
In low-fluid-level wells, prior designs that allow the element to deflate by displacement into the tubing have presented a problem since the hydrostatic head in the tubing could prevent element deflation. The apparatus of the present invention allows element deflation into the annulus.
The apparatus of the present invention is constructed simply and is operable by pressure developed at the surface. It also allows operations such as injection to go on below the set packer element while, at the same time, locking in the pressure behind the element to ensure it has a solid grip on the well bore or casing.